Polymer, rubber composition containing polymer, crosslinked rubber composition obtained by crosslinking rubber composition, and tire having crosslinked rubber composition

ABSTRACT

Provided are: a polymer capable of providing a crosslinked rubber composition with improved durability (i.e., breaking resistance, abrasion resistance, and crack growth resistance) and a method for producing the same, a rubber composition containing the polymer, a crosslinked rubber composition obtained by crosslinking the rubber composition, and a tire having the crosslinked rubber composition. The polymer is either a synthesized polyisoprene or an isoprene copolymer, and contains a residual catalyst in an amount of 300 ppm or less.

TECHNICAL FIELD

The present invention relates to a polymer, a rubber compositioncontaining the polymer, a crosslinked rubber composition obtained bycrosslinking the rubber composition, and a tire having the crosslinkedrubber composition; and in particular, to a polymer capable of providinga crosslinked rubber composition with improved durability (i.e.,breaking resistance, abrasion resistance, and crack growth resistance),a rubber composition containing such a polymer, a crosslinked rubbercomposition obtained by crosslinking the rubber composition, and a tirehaving the crosslinked rubber composition.

BACKGROUND ART

In light of the recent social demand for saving energy and resources,rubber materials with high breaking resistance, high abrasionresistance, and high crack growth resistance are now desired commonly torespond to the demand for tires with improved durability. Further, asurge in natural rubber prices has created a need for developingsynthetic rubber that exhibits durability equal to that of naturalrubber.

To enhance durability of the synthetic rubber, the cis content ofsynthetic polyisoprene is conventionally increased to improvestrain-induced crystallinity. Refer, for example, to JP 2004-27179 A(PTL 1) and WO 2006/078021 (PTL 2). However, the synthetic rubberimproved in this manner is still less durable than natural rubber whensubjected to higher severity conditions.

Furthermore, a polymer having an isoprene skeleton is likely to showmain-chain breaks compared to a polymer composed of other monomers. Thismain-chain break is considered causing the less durability of thepolymer under high severity conditions. Additionally, in synthesizing apolymer to impart high-molecular weight, the chain ends of the polymermay be denatured with tin tetrachloride or titanium tetrachloride. Thisdenaturation involves gelation commonly, thereby significantly reducingthe durability of the polymer.

CITATION LIST Patent Literature

PTL 1: JP 2004-27179 A

PTL 2: WO 2006/078021

SUMMARY OF INVENTION Technical Problem

In light of the above, an object of the present invention is to providea polymer capable of providing a crosslinked rubber composition withimproved durability (i.e., breaking resistance, abrasion resistance, andcrack growth resistance), a rubber composition containing such apolymer, a crosslinked rubber composition obtained by crosslinking therubber composition, and a tire having the crosslinked rubbercomposition.

Solution to Problem

The inventors of the present invention have found that a residualcatalyst remaining in a polymer (at least one of a synthesizedpolyisoprene and an isoprene copolymer) by a certain reduced amount isless likely to inhibit crosslinking reaction of the polymer duringvulcanization and that such a polymer with less amount of residualcatalyst can provide a crosslinked rubber composition with durability(i.e., breaking resistance, abrasion resistance, and crack growthresistance) higher than that of conventional synthetic rubber, and havemade the present invention.

The polymer of the present invention, being a synthesized polyisopreneor a isoprene copolymer, thus has a residual catalyst in an amount of300 ppm or less. The polymer having 300 ppm or less residual catalystcan further reliably form a network structure when the rubbercomposition containing the polymer is in vulcanization.

A “synthesized polyisoprene” as used herein means an isoprenehomopolymer obtained by polymerizing (or synthesizing) isoprenemonomers. An “isoprene copolymer” as used herein means a copolymercomposed of isoprene and a compound other than isoprene. The isoprenecopolymer is obtained by polymerizing (or synthesizing) isoprenemonomers and monomers of a compound other than isoprene. Both“synthesized polyisoprene” and “isoprene copolymer” encompass polymershaving part of their polymer chains being denatured.

In producing the polymer of the present invention, it is particularlypreferable to reduce the residual catalyst when the polymerizationcatalyst used is a catalyst derived from a Lewis acid. Examples of thecatalyst derived from a Lewis acid include, as will be discussed indetail below, a boron-containing halogenated compound, such as B(C₆F₅)₃,and aluminum-containing halogenated compound, such as Al(C₆F₅)₃, whichare frequently used as polymerization catalysts. The catalysts derivedfrom a Lewis acid are known to inhibit a vulcanization accelerationeffect caused by a vulcanization accelerator, and thus the residualamount thereof is particularly desired to be small.

In the polymer of the present invention, 3,4-vinyl bond content in anisoprene-derived unit in the synthesized polyisoprene or the isoprenecopolymer is preferably 5% or less.

The synthesized polyisoprene or the isoprene copolymer having 3,4-vinylbond content of 5% or less in its isoprene-derived unit cansignificantly improve its durability.

The term “3,4-vinyl bond content” as used herein refers to the ratio ofthe 3,4-vinyl structure to the whole isoprene unit in the synthesizedpolyisoprene or in the isoprene copolymer. The same definition appliesto the terms “cis-1,4 bond content”, “trans-1,4 bond content”, and“1,2-vinyl bond content” as used herein.

A rubber composition of the present invention contains a rubberingredient that at least contains the polymer of the present invention.

The rubber composition containing at least the polymer of the presentinvention significantly increases the strain-induced crystallinity,thereby providing a crosslinked rubber composition with improveddurability (i.e., breaking resistance, abrasion resistance, and crackgrowth resistance).

The phrase “containing at least the polymer of the present invention”means that the rubber composition contains at least one of thesynthesized polyisoprene and the isoprene copolymer.

The rubber composition of the present invention preferably has a totalcontent of the polymer in the rubber ingredient in an amount of 15 to100 mass %.

The rubber ingredient having the total polymer amount of 15 to 100 mass% allows the polymer to satisfactorily exhibit the effect of theimproved strain-induced crystallinity.

The rubber composition of the present invention further contains afiller. The content of the filler is preferably 10 to 75 mass parts per100 mass parts of the rubber ingredient.

The rubber composition containing the filler in an amount of 10 to 75mass parts per 100 mass parts rubber ingredient can exhibit its effectand can be blended into the rubber ingredient satisfactorily.

The rubber composition having the filler content exceeding 75 mass partsper 100 mass parts of the rubber ingredient may impair the workability.

A crosslinked rubber composition of the present invention is obtained bycrosslinking the rubber composition of the present invention.

The crosslinked rubber composition obtained by crosslinking the rubbercomposition improves the durability (i.e., breaking resistance, abrasionresistance, and crack growth resistance) of the crosslinked rubbercomposition.

The tire of the present invention contains the crosslinked rubbercomposition of the present invention.

The tire having the crosslinked rubber composition can improve thedurability (i.e., breaking resistance, abrasion resistance, and crackgrowth resistance) of the tire.

The tire of the present invention includes a tread member having thecrosslinked rubber composition of the present invention.

The tire including a tread member that has the crosslinked rubbercomposition can improve the durability (i.e., breaking resistance,abrasion resistance, and crack growth resistance) of the tread member.

Advantageous Effect of Invention

The present invention provides the polymer capable of providing thecrosslinked rubber composition with improved durability (i.e., breakingresistance, abrasion resistance, and crack growth resistance), therubber composition containing such a polymer, the crosslinked rubbercomposition obtained by crosslinking the rubber composition, and thetire having the crosslinked rubber composition.

DESCRIPTION OF EMBODIMENTS

(Polymer)

The polymer of the present invention is a synthesized polyisoprene or anisoprene copolymer.

The catalyst contains a residual catalyst in an amount of 300 ppm (ratioby weight) or less. In particular, the amount of the residual catalystis more preferably 200 ppm (ratio by weight) or less, and mostpreferably 100 ppm (ratio by weight) or less.

The residual catalyst remaining in the polymer in an amount of 300 ppmor less does not either inhibit the formation of a network structurewhen the rubber composition containing the polymer is vulcanized norreduce the strain-induced crystallinity and durability.

The polymer having the residual catalyst in an amount of the above “morepreferable” or “most preferable” range is advantageous in terms offorming the network structure.

The amount of the residual catalyst can be measured, for example, byperforming element analysis on the residual metals (e.g., aluminium andgadolimium) in the polymer.

The catalyst will be discussed in detail below upon describing themethod of producing the polymer.

The number average molecular weight (Mn) of the polymer is notparticularly limited and may be selected as appropriate depending on theapplication thereof. Preferably, the number average molecular weight is1.5 million or more, and more preferably 1.5 to 2.0 million. The polymerhaving the number average molecular weight (Mn) of 1.5 million or morecan further improve the durability (i.e., breaking resistance, abrasionresistance, and crack growth resistance) of the crosslinked rubbercomposition, while the polymer having the number average molecularweight (Mn) of 2.0 million or less can maintain the processability. Thepolymer having the number average molecular weight (Mn) within the above“more preferable” or “most preferable” range is advantageous in terms ofboth the durability and processability.

The number average molecular weight (Mn) is measured in terms ofpolystyrene, referencing polystyrene as a standard substance, by usinggel permeation chromatography (GPC) at a temperature of 140° C.

The polymer having the number average molecular weight (Mn) of 1.5million or more is obtained by performing a polymerization at a lowtemperature (i.e., −50 to 100° C.) for a predetermined time (i.e., 30minutes to 2 days), using a polymerization catalyst, or a first, asecond, or a third polymerization catalyst composition, which will bedescribed below.

Further, molecular weight distribution (Mw/Mn), represented by the ratiobetween the weight average molecular weight (Mw) and the number averagemolecular weight (Mn), is not particularly limited and may be selectedas appropriate depending on the application thereof. Preferably, themolecular weight distribution is 5.0 or less, more preferably 4.0 orless, and most preferably 3.5 or less. The molecular weight distribution(Mw/Mn) exceeding 5.0 may make the physical property inhomogeneous. Themolecular weight distribution (Mw/Mn) within the above “more preferable”or “most preferable” range is advantageous in terms of low-lossperformance. Mw and Mn are obtained by gel permeation chromatography(GPC) using polystyrene as a standard substance, and the molecularweight distribution (Mw/Mn) is calculated from the results thereof.

The gel fraction in the polymer is not particular limited and may beselected as appropriate depending on the application thereof. However,the gel fraction is preferably 40% or less, more preferably 20% or less,and most preferably 10% or less.

The polymer having the gel fraction of 40% or less can prevent asignificant deterioration of durability.

The polymer having the gel fraction within the above “more preferable”or “most preferable” range is advantageous in terms of durability.

The polymer having 40% or less gel fraction is obtained by performing apolymerization at a low temperature (−50 to 100° C.) for a predeterminedtime (30 minutes to 2 days), using the polymerization catalyst, or thefirst, second, or third polymerization catalyst composition, which willbe described below.

The gel fraction (unit: %) as used herein means a value obtained by:measuring a differential refractive index (RI) Ss (unit: m second) of astandard sample (gel fraction=0%), which is a filtrate obtained bypassing a THF solution of a polymer through a filter of GPC with a poresize of 0.45 μm; and using a calibration curve with the concentration(unit: mg/g) of the polymer in the THF solution on the horizontal axisand the differential refractive index (RI) Ss (unit: m second) on thevertical axis. Specifically, the gel fraction is calculated by passing aTHF solution of a target polymer, for which the gel fraction is to beobtained, through the above filter to measure a differential refractiveindex (RI) Sx (unit: m second) of the solution; calculating thedifferential refractive index (RI) Ss (unit: m second) of the standardsample (gel fraction=0%) of the concentration (unit: mg/g) of the THFsolution containing the target polymer for which the gel fraction is tobe obtained, using the calibration curve prepared in advance; andsubstituting the measured Sx and the calculated Ss into the followingexpression (X):

Gel fraction (%)={(Ss×Sx)/Ss}×100  (X)

A nitrogen content in the polymer is not particularly limited and may beselected as appropriate depending on the application thereof. However,the nitrogen content is preferably less than 0.02 mass % and morepreferably 0 mass %.

The polymer having the nitrogen content of less than 0.02% or lessallows its protein-derived nitrogen content to be also less than 0.02mass %. This low content can minimize the protein-related gelgeneration, thereby reducing the gel fraction.

The nitrogen content can be measured, for example, by performing elementanalysis.

<Synthesized Polyisoprene>

—Cis-1,4 Bond Content—

The cis-1,4 bond content of the synthesized polyisoprene is notparticularly limited and may be selected as appropriate depending on theapplication thereof. However, the bond content is preferably 96% ormore, more preferably 97% or more, and most preferably 99% or more.

The synthesized polyisoprene having the cis-1,4 bond content of 96% ormore can have polymer chains be oriented in an intended manner, therebyachieving sufficient strain-induced crystallinity. The synthesizedpolyisoprene having the cis-1,4 bond content exceeding 99% achievesstrain-induced crystallinity sufficient for obtaining still higherdurability.

—Trans-1,4 Bond Content—

The trans-1,4 bond content of the synthesized polyisoprene is notparticularly limited and may be selected as appropriate depending on theapplication thereof. However, the bond content is preferably is 5% orless, more preferably 3% or less, and most preferably 1% or less.

The synthesized polyisoprene having the trans-1,4 bond content of 5% orless can develop strain-induced crystallinity.

—3,4-Vinyl Bond Content—

The 3,4-vinyl bond content of the synthesized polyisoprene is notparticularly limited and may be selected as appropriate depending on theapplication thereof. The bond content is preferably is 5% or less, morepreferably 3% or less, and most preferably 1% or less.

The synthesized polyisoprene having the 3,4-vinyl bond content of 5% orless can develop strain-induced crystallinity.

The synthesized polyisoprene having the 3,4-vinyl bond content of 5% orless can be obtained by polymerizing isoprene monomers at a lowtemperature (i.e., −50 to 100° C.) for a predetermined time (i.e., 30minutes to 2 days), using the polymerization catalyst, or the first,second, or third polymerization catalyst composition, which will bediscussed below.

—Method of Producing Synthesized Polyisoprene—

Next, a method of producing the synthesized polyisoprene will bedescribed in detail. However, the producing method described in detailbelow is merely an example. The synthesized polyisoprene can be producedby polymerizing isoprene monomers in the presence of the polymerizationcatalyst or the polymerization catalyst composition.

The method of producing the synthesized polyisoprene includes at least apolymerization step, and further includes coupling, cleaning, and othersteps arbitrarily selected as necessary.

—Polymerization Step—

The polymerization step is a step for polymerizing isoprene monomers.

In the polymerization step, isoprene monomers can be polymerized in amanner similar to that conventionally used in producing polymers using acoordination ion polymerization catalyst, except that the polymerizationcatalyst, or the first, second, or third polymerization catalystcomposition, which will be discussed below, is used. The polymerizationcatalyst or the polymerization catalyst compositions used in the presentinvention will be described in detail below.

The catalyst that may be used in the polymerization step is thepolymerization catalyst, or the first, second, or third polymerizationcatalyst composition, which will be described below.

An arbitrary method can be employed as the polymerization methodincluding, for example, solution polymerization, suspensionpolymerization, liquid phase bulk polymerization, emulsionpolymerization, vapor phase polymerization, and solid statepolymerization. In addition, in the case of using a solvent forpolymerization reaction, any solvent may be used that is inert to thepolymerization reaction, including, for example, toluene, cyclohexane,n-hexane and mixtures thereof.

In the case of using a polymerization catalyst composition, thepolymerization step can be carried out in either one of the followingmanners. That is, for example, (1) the components forming thepolymerization catalyst composition may be provided in thepolymerization reaction system containing isoprene monomers separately,to thereby prepare the polymerization catalyst composition in thereaction system, or (2) the polymerization catalyst composition preparedin advance may be provided into the polymerization reaction system.Further, the manner (2) also includes providing the metallocene complex(active species) activated by a co-catalyst.

Further, in the polymerization step, a terminator such as methanol,ethanol, and isopropanol may be used to stop the polymerization.

In the polymerization step, the polymerization reaction of the isoprenemay preferably performed in an inert gas atmosphere, and preferably innitrogen or argon atmosphere. The polymerization temperature of thepolymerization reaction is not particularly limited, and preferably in arange of, for example, −100 to 200° C., and may also be set totemperatures around room temperature. An increase in the polymerizationtemperature may reduce the cis-1,4-selectivity in the polymerizationreaction. The polymerization reaction is preferably performed underpressure in a range of 0.1 to 10.0 MPa so as to allow the isoprene to besufficiently introduced into polymerization system. Further, thereaction time of the polymerization is not particularly limited, and maypreferably be in a range of, for example, 1 second to 10 days, which maybe selected as appropriate depending on the conditions such as the typeof the catalyst, and the polymerization temperature.

—First Polymerization Catalyst Composition—

One example of the first polymerization catalyst composition contains atleast one complex selected from the group consisting of: a metallocenecomplex represented by the general formulae (I), a metallocene complexrepresented by the following general formula (II), and a halfmetallocene cation complex represented by the general formula (III).

In the Formula (I), M represents a lanthanoid element, scandium, oryttrium; Cp^(R) each independently represents a unsubstituted orsubstituted indenyl, R^(a) to R^(f) each independently represents ahydrogen atom or alkyl group having 1 to 3 carbon atoms; L represents aneutral Lewis base; and w represents an integer of 0 to 3.

In the Formula (II), M represents a lanthanoid element, scandium, oryttrium; Cp^(R) each independently represents an unsubstituted orsubstituted indenyl; X′ represents a hydrogen atom, a halogen atom, analkoxide group, a thiolate group, an amide group, a silyl group, or ahydrocarbon group having 1 to 20 carbon atoms; L represents a neutralLewis base; and w represents an integer of 0 to 3.

In the Formula (III), M represents a lanthanoid element, scandium, oryttrium; Cp^(R′) represents an unsubstituted or substitutedcyclopentadienyl, indenyl, fluorenyl; X represents a hydrogen atom, ahalogen atom, an alkoxide group, a thiolate group, an amide group, asilyl group, or a hydrocarbon group having 1 to 20 carbon atoms; Lrepresents a neutral Lewis base; w represents an integer of 0 to 3; and[B]⁻ represents a non-coordinating anion.

The first polymerization catalyst composition may further includeanother component, such as a co-catalyst, which is contained in aregular polymerization catalyst composition containing a metallocenecomplex. Here, the metallocene complex is a complex compound having atleast one or more cyclopentadienyl groups or derivative ofcyclopentadienyl groups bonded to the central metal. In particular, ametallocene complex may be referred to as half metallocene complex whenthe number of cyclopentadienyl group or derivative thereof bonded to thecentral metal is one.

In the polymerization system, the concentration of the complex containedin the first polymerization catalyst composition is preferably in arange of 0.1 mol/L to 0.0001 mol/L.

In the metallocene complex represented by the general formulae (I) and(II) above, Cp^(R) in the formulae represents an unsubstituted orsubstituted indenyl group. Cp^(R) having an indenyl ring as a basicskeleton may be represented by C₉H_(7-X)R_(X) or C₉H_(11-X)R_(X). Here,X represents an integer of 0 to 7 or 0 to 11. R each independentlypreferably represents a hydrocarbyl group or a metalloid group. Thehydrocarbyl group preferably has 1 to 20 carbon atoms, more preferably 1to 10 carbon atoms, and still more preferably 1 to 8 carbon atoms.Preferred specific examples of the hydrocarbyl group include a methylgroup, an ethyl group, a phenyl group, and a benzyl group. Examples ofmetalloid in the metalloid group include germyl (Ge), stannyl (Sn), andsilyl (Si). The metalloid group preferably has a hydrocarbyl group, andexamples of such a hydrocarbyl group are similar to those listed above.Specific example of the metalloid group includes a trimethylsilyl group.Specific examples of the substituted indenyl group include 2-phenylindenyl and 2-methyl indenyl group. Two Cp^(R) in each of the generalformulae (I) and (II) may be the same as or different from each other.

In the half metallocene cation complex represented by the generalformula (III), Cp^(R′) in the formula represents a substituted orunsubstituted cyclopentadienyl, indenyl, or fluorenyl group, with thesubstituted or unsubstituted indenyl group being preferred. Cp^(R′)having a cyclopentadienyl ring as a basic skeleton is represented byC₅H_(5-X)R_(X), wherein X represents an integer of 0 to 5. R eachindependently preferably represents a hydrocarbyl group or a metalloidgroup. The hydrocarbyl group preferably has 1 to 20 carbon atoms, morepreferably 1 to 10 carbon atoms, and still more preferably 1 to 8 carbonatoms. Preferred specific examples of the hydrocarbyl group include amethyl group, an ethyl group, a phenyl group, and a benzyl group.Examples of metalloid in the metalloid group include germyl (Ge),stannyl (Sn), and silyl (Si). The metalloid group preferably has ahydrocarbyl group, and the examples of such a hydrocarbyl group aresimilar to those listed above. Specific examples of the metalloid groupinclude a trimethylsilyl group. Specific examples of Cp^(R′) having acyclopentadienyl ring as a basic skeleton include the following:

wherein R represents a hydrogen atom, a methyl group, or an ethyl group.In the general formula (III), Cp^(R′) having an indenyl ring as a basicskeleton is defined in a manner similar to Cp^(R) in the general formula(I), and preferred examples thereof are also defined in a manner similarto Cp^(R) in the general formula (I).

In the general formula (III), Cp^(R′) having the fluorenyl ring as abasic skeleton may be represented by C₁₃H_(9-X)R_(X) orC₁₃H_(17-X)R_(X), wherein X represents an integer of 0 to 9 or 0 to 17.Preferably, R each independently represents a hydrocarbyl group or ametalloid group. The hydrocarbyl group preferably has 1 to 20 carbonatoms, more preferably 1 to 10 carbon atoms, and still more preferably 1to 8 carbon atoms. Preferred specific examples of the hydrocarbyl groupinclude a methyl group, an ethyl group, a phenyl group, and a benzylgroup. Examples of metalloid in the metalloid group include germyl (Ge),stannyl (Sn), and silyl (Si). The metalloid group preferably has ahydrocarbyl group, and the examples of such a hydrocarbyl group aresimilar to those listed above. Specific examples of the metalloid groupinclude a trimethylsilyl group.

The central metal represented by M in the general formulae (I), (II),and (III) represents a lanthanoid element, scandium, or yttrium. Thelanthanoid elements include 15 elements with atomic numbers 57 to 71,and may be any one of them. Preferred examples of the central metalrepresented by M include samarium (Sm), neodymium (Nd), praseodymium(Pr), gadolinium (Gd), cerium (Ce), holmium (Ho), scandium (Sc), andyttrium (Y).

The metallocene complex represented by the general formula (I) includesa silyl amide ligand represented by [—N(SiR₃)₂]. Groups represented by R(R^(a) to R^(f) in the general formula (I)) in the silyl amide ligandeach independently represent a hydrogen atom or an alkyl group having 1to 3 carbon atoms. It is preferred that at least one of R^(a) to R^(f)represents a hydrogen atom. With at least one of R^(a) to R^(f) being ahydrogen atom, the catalyst can be synthesized with ease, and the heightaround silicon can be reduced, thereby allowing the unconjugated olefinto be easily introduced. For the same reason, at least one of R^(a) toR^(c) is preferably a hydrogen atom, and at least one of R^(d) to R^(f)is more preferably a hydrogen atom. Further, the alkyl group ispreferably a methyl group.

The metallocene complex represented by the general formula (II) includesa silyl ligand represented by [—SiX′₃]. X′ in the silyl ligandrepresented by [—SiX′₃] is a group defined in a manner similar to X inthe general formula (III) which will be described below, and preferredexamples thereof are also defined in a manner similar to X in thegeneral formula (III).

In the general formula (III), X represents a group selected from thegroup consisting of a hydrogen atom, a halogen atom, an alkoxide group,a thiolate group, an amide group, a silyl group, and a hydrocarbon grouphaving 1 to 20 carbon atoms. Here, the alkoxy group may be any one of:aliphatic alkoxy groups, such as a methoxy group, an ethoxy group, apropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxygroup, and a tert-butoxy group; and aryl oxide groups, such as a phenoxygroup, a 2,6-di-tert-butylphenoxy group, a 2,6-diisopropylphenoxy group,a 2,6-dineopentylphenoxy group, a 2-tert-butyl-6-isopropylphenoxy group,a 2-tert-butyl-6-neopentylphenoxy group, and a2-isopropyl-6-neopentylphenoxy group, with the 2,6-di-tert-butylphenoxygroup being preferred.

In the general formula (III), the thiolate group represented by X may beany one of: aliphatic thiolate groups such as a thiomethoxy group, athioethoxy group, a thiopropoxy group, a thio-n-butoxy group, athioisobutoxy group, a thio-sec-butoxy group, and a thio-tert-butoxygroup; and aryl thiolate groups such as a thiophenoxy group, a2,6-di-tert-butylthiophenoxy group, a 2,6-diisopropylthiophenoxy group,a 2,6-dineopentylthiophenoxy group, a2-tert-butyl-6-isopropylthiophenoxy group, a2-tert-butyl-6-thioneopentylphenoxy group, a2-isopropyl-6-thioneopentylphenoxy group, and a2,4,6-triisopropylthiophenoxy group, with the2,4,6-triisopropylthiophenoxy group being preferred.

In the general formula (III), the amide group represented by X may beany one of: aliphatic amide groups such as a dimethyl amide group, adiethyl amide group, and a diisopropyl amide group; arylamide groupssuch as a phenyl amide group, a 2,6-di-tert-butylphenyl amide group, a2,6-diisopropylphenyl amide group, a 2,6-dineopentylphenyl amide group,a 2-tert-butyl-6-isopropylphenyl amide group, a2-tert-butyl-6-neopentylphenyl amide group, a2-isopropyl-6-neopentylphenyl amide group, and a2,4,6-tri-tert-butylphenyl amide group; and bistrialkylsilyl amidegroups such as a bistrimethylsilyl amide group, with thebistrimethylsilyl amide group being preferred.

In the general formula (III), the silyl group represented by X may beany one of a trimethylsilyl group, a tris(trimethylsilyl)silyl group, abis(trimethylsilyl)methylsilyl group, a trimethylsilyl(dimethyl)silylgroup, and a triisopropylsilyl(bistrimethylsilyl)silyl group, with thetris(trimethylsilyl)silyl group being preferred.

In the general formula (III), the halogen atom represented by X may beany one of a fluorine atom, a chlorine atom, a bromine atom, and aniodine atom, with the chlorine atom and the bromine atom beingpreferred. Specific examples of the hydrocarbon group having 1 to 20carbon atoms include: linear or branched aliphatic hydrocarbon groupssuch as a methyl group, an ethyl group, an n-propyl group, an isopropylgroup, an n-butyl group, an isobutyl group, a sec-butyl group, atert-butyl group, a neopentyl group, a hexyl group, and an octyl group;aromatic hydrocarbon groups such as a phenyl group, a tolyl group, and anaphthyl group; aralkyl groups such as a benzyl group; and hydrocarbongroups such as a trimethylsilylmethyl group and abistrimethylsilylmethyl group each containing a silicon atom, with themethyl group, the ethyl group, the isobutyl group, thetrimethylsilylmethyl group, and the like being preferred.

In the general formula (III), X is preferably the bistrimethylsilylamide group or the hydrocarbon group having 1 to 20 carbon atoms.

In the general formula (III), one example of the non-coordinating anionrepresented by [B]⁻ is for example tetravalent boron anions. Examples ofthe tetravalent boron anion include tetraphenyl borate,tetrakis(monofluorophenyl)borate, tetrakis(difluorophenyl)borate,tetrakis(trifluorophenyl)borate, tetrakis(tetrafluorophenyl)borate,tetrakis(pentafluorophenyl)borate,tetrakis(tetrafluoromethylphenyl)borate, tetra(tolyl)borate,tetra(xylyl)borate, (triphenyl, pentafluorophenyl)borate,[tris(pentafluorophenyl), phenyl]borate, andtridecahydride-7,8-dicarbaundecaborate, with thetetrakis(pentafluorophenyl)borate being preferred.

The metallocene complexes represented by the general formulae (I) and(II) and the half metallocene cation complex represented by the generalformula (III) may include 0 to 3, preferably 0 or 1 neutral Lewis basesrepresented by L. Examples of the neutral Lewis base L includetetrahydrofuran, diethyl ether, dimethylaniline, trimethylphosphine,lithium chloride, neutral olefins, and neutral diolefins. When thecomplex contains multiple neutral Lewis bases represented by L, thebases L may be the same as or different from each other.

The metallocene complexes represented by the general formulae (I) and(II), and the half metallocene cation complex represented by the generalformula (III) may be contained as monomers, or as dimers or multimershaving two or more monomers.

The metallocene complex represented by the general formula (I) can beobtained by, for example, subjecting a lanthanoid trishalide, a scandiumtrishalide, or a yttrium trishalide to reaction in a solvent with a saltof indenyl (for example, a potassium salt or a lithium salt) and a saltof bis(trialkylsilyl)amide (for example, a potassium salt or a lithiumsalt). The reaction may be carried out at temperatures around roomtemperature, and thus the metallocene-based composite catalyst can beproduced under mild conditions. The reaction time is arbitrary, butabout several hours to several tens of hours. The reaction solvent isnot particularly limited, and any solvent including, for exampletoluene, which is capable of dissolving the raw material and theproduct, can be preferably used. In the following, a reaction examplefor obtaining the metallocene complex represented by the general formula(I) is described.

In the above formula, X″ represents a halide.

The metallocene complex represented by the general formula (II) can beobtained by, for example, subjecting a lanthanoid trishalide, a scandiumtrishalide, or a yttrium trishalide to reaction in a solvent with a saltof indenyl (for example, a potassium salt or a lithium salt) and a saltof silyl (for example, a potassium salt or a lithium salt). The reactionmay be carried out at temperatures around room temperature, and thus themetallocene-based composite catalyst can be produced under mildconditions. The reaction time is arbitrary, but about several hours toseveral tens of hours. The reaction solvent is not particularly limited,but is preferably a solvent capable of dissolving the raw material andthe product. Toluene may be for example used. In the following, areaction example for obtaining the metallocene complex represented bythe general formula (II) is described.

In the above formula, X″ represents a halide.

The half metallocene cation complex represented by the general formula(III) can be obtained by, for example, the following reaction:

In formula (IV), M represents a lanthanoid element, scandium, oryttrium; Cp^(R′) independently represents an unsubstituted orsubstituted cyclopentadienyl, indenyl, or fluorenyl; X represents ahydrogen atom, a halogen atom, an alkoxide group, a thiolate group, anamide group, a silyl group, or a hydrocarbon group having 1 to 20 carbonatoms; L represents a neutral Lewis base; and w represents an integer of0 to 3. Further, in the general formula [A]⁺[B]⁻ representing an ioniccompound, [A]⁺ represents a cation; and [B]⁻ represents anon-coordinating anion.

Examples of the cation represented by [A]⁺ include a carbonium cation,an oxonium cation, an amine cation, a phosphonium cation, acycloheptatrienyl cation, and a ferrocenium cation containing atransition metal. Examples of the carbonium cation includetrisubstituted carbonium cations such as a triphenylcarbonium cation anda tri(substituted phenyl)carbonium cation. Specific examples of thetri(substituted phenyl)carbonium cation include atri(methylphenyl)carbonium cation. Examples of the amine cation include:trialkylammonium cations such as a trimethylammonium cation, atriethylammonium cation, a tripropylammonium cation, and atributylammonium cation; N,N-dialkylanilinium cations such as aN,N-dimethylanilinium cation, a N,N-diethylanilinium cation, and aN,N-2,4,6-pentamethylanilinium cation; and dialkylammonium cations suchas a diisopropylammonium cation and a dicyclohexylammonium cation.Examples of the phosphonium cation include triarylphosphonium cationssuch as a triphenylphosphonium cation, a tri(methylphenyl)phosphoniumcation, and a tri(dimethylphenyl)phosphonium cation. Of those cations,the N,N-dialkylanilinium cations or the carbonium cations are preferred,and the N,N-dialkylanilinium cations are particularly preferred.

The ionic compound, represented by the general formula [A]⁺[B]⁻, used inthe above reaction is a compound obtained by combining any one selectedfrom the non-coordinating anions described above and any one selectedfrom the cations described above. Preferred examples thereof includeN,N-dimethylanilinium tetrakis(pentafluorophenyl)borate andtriphenylcarbonium tetrakis(pentafluorophenyl)borate. The ionic compoundrepresented by the general formula [A]⁺[B]⁻ is added to the metallocenecomplex in an amount of preferably 0.1-fold mol to 10-fold mol and morepreferably in an amount of about 1-fold mol. When the half metallocenecation complex represented by the general formula (III) is used inpolymerization reaction, the half metallocene cation complex representedby the general formula (III) may be supplied to the polymerizationsystem by itself; or alternatively, the compound represented by thegeneral formula (IV) and the ionic compound represented by the generalformula [A]⁺[B]⁻ may be separately supplied to the polymerizationsystem, to thereby form the half metallocene cation complex representedby the general formula (III) in the reaction system. In addition, thehalf metallocene cation complex represented by the general formula (III)may be formed in the reaction system by using the metallocene complexrepresented by the general formula (I) or (II) and the ionic compoundrepresented by the general formula [A]⁺[B]⁻ in combination.

Structures of the metallocene complex represented by the general formula(I) and (II) and the half metallocene cation complex represented by thegeneral formula (III) are preferably determined by X-raycrystallography.

The co-catalyst that can be contained in the first polymerizationcatalyst composition may be arbitrarily selected from components used asthe co-catalyst for a regular polymerization catalyst compositioncontaining a metallocene complex. Preferred examples of the co-catalystinclude aluminoxanes, organic aluminum compounds, and the above ioniccompounds. These co-catalysts may be contained alone or in combinationof two or more.

The aluminoxane is preferably an alkyl aluminoxane. Examples of thealkyl aluminoxane include methyl aluminoxane (MAO) and modified methylaluminoxanes. One preferred example of the modified methylaluminoxaneincludes MMAO-3A (manufactured by Tosoh Finechem Corporation). Thecontent of aluminoxane in the first polymerization catalyst compositionis preferably about 10 to 1,000, or more preferably about 100, at anelement ratio (Al/M) of the aluminum element Al of the aluminoxane tothe center metal M of the metallocene complex.

A preferred example of the organic aluminum compounds is represented bya general formula AlRR′R″ (wherein R and R′ each independently representa hydrocarbon group of C1 to C10 or a hydrogen atom, and R″ is ahydrocarbon group of C1 to C10). Examples of the organic aluminumcompound include a trialkyl aluminum, a dialkyl aluminum chloride, analkyl aluminum dichloride, and a dialkyl aluminum hydride, with thetrialkyl aluminum being preferred. Further, examples of the trialkylaluminum include triethyl aluminum and triisobutyl aluminum. The contentof the organic aluminum compound in the above polymerization catalystcomposition is preferably 1-fold mol to 50-fold mol and more preferablyabout 10-fold mol, relative to the metallocene complex.

In the polymerization catalyst composition, the metallocene complexrepresented by the general formulae (I) and (II) and the halfmetallocene complex represented by the general formula (III) may becombined with an appropriate co-catalyst, to thereby increase thecis-1,4 bond content and the molecular weight of a polymer to beobtained.

—Second Polymerization Catalyst Composition—

Next, the second polymerization catalyst composition will be described.

A preferred example of the second polymerization catalyst compositionmay include:

component (A): a rare earth element compound or a reactant of the rareearth element compound and a Lewis base, with no bond formed between therare earth element and carbon;

component (B): at least one selected from a group consisting of: anionic compound (B-1) composed of a non-coordinating anion and a cation;an aluminoxane (B-2); and at least one kind of halogen compound (B-3)from among a Lewis acid, a complex compound of a metal halide and aLewis base, and an organic compound containing active halogen. Further,if the second polymerization catalyst composition contains at least onekind of the ionic compound (B-1) and the halogen compound (B-3), thepolymerization catalyst composition further contains:

component (C): an organic metal compound represented by the followinggeneral formula (X):

YR¹ _(a)R² _(b)R³ _(c)  (X)

wherein: Y is a metal selected from Group 1, Group 2, Group 12, andGroup 13 of the periodic table; R1 and R2 are the same or differenthydrocarbon groups each having 1 to 10 carbon atoms or a hydrogen atom;and R3 is a hydrocarbon group having 1 to 10 carbon atoms, in which R3may be the same as or different from R1 or R2 above, with a being 1 andb and c both being 0 when Y is a metal selected from Group 1 of theperiodic table, a and b being 1 and c being 0 when Y is a metal selectedfrom Group 2 and Group 12 of the periodic table, a, b, and c are all 1when Y is a metal selected from Group 13 of the periodic table.

The second polymerization catalyst composition used in the producingmethod is required to contain the above components (A) and (B), and ifthe polymerization catalyst composition contains at least one of theabove ionic compound (B-1) and halogen compound (B-3), then it isfurther required to contain an organometallic compound represented bythe following formula:

YR¹ _(a)R² _(b)R³ _(c)  (X)

wherein: Y is a metal selected from Group 1, Group 2, Group 12, andGroup 13 of the periodic table; R1 and R2 are the same or differenthydrocarbon groups each having 1 to 10 carbon atoms or a hydrogen atom;and R3 is a hydrocarbon group having 1 to 10 carbon atoms, in which R3may be the same as or different from R1 or R2 above, with a being 1 andb and c both being 0 when Y is a metal selected from Group 1 of theperiodic table, a and b being 1 and c being 0 when Y is a metal selectedfrom Group 2 and Group 12 of the periodic table, a, b, and c are all 1when Y is a metal selected from Group 13 of the periodic table.

The ionic compound (B-1) and the halogen compound (B-3) do not havecarbon atoms to be fed to the component (A), and thus the component (C)becomes necessary as a source of feeding carbon to the component (A).Here, the polymerization catalyst composition still may include thecomponent (C) even if the polymerization catalyst composition includesthe aluminoxane (B-2). Further, the second polymerization catalystcomposition may further include another component such as a co-catalyst,which is contained in a regular general rare earth elementcompound-based polymerization catalyst composition.

In the polymerization system, the concentration of the component (A)contained in the second polymerization catalyst composition ispreferably in a range of 0.1 to 0.0001 mol/L.

The component (A) contained in the second polymerization catalystcomposition is a rare earth element compound or a reactant of the rareearth element compound and a Lewis base. Here, the rare earth elementcompound and the reactant of the rare earth element compound and a Lewisbase do not have a direct bond of the rare earth element and carbon.When the rare earth element compound or a reactant thereof does not havea direct bond formed between a rare earth element and carbon, theresulting compound is stable and easy to handle. Here, the rare earthelement compound refers to a compound containing a lanthanoid element,scandium, or yttrium. The lanthanoid elements include elements withatomic numbers 57 to 71 of the periodic table. Specific examples of thelanthanoid element include lanthanum, cerium, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, and lutetium. These components (A)may be contained alone or in combination of two or more.

The rare earth element compound is preferably composed of a rare earthmetal of a bivalent or trivalent salt or of a complex compound, andfurther preferably a rare earth element compound containing at least oneligand selected from a hydrogen atom, a halogen atom, and an organiccompound residue. Further, the rare earth element compound or thereactant of the rare earth element compound and the Lewis base isrepresented by the following general formula (XI) or (XII):

M¹¹X¹¹ ₂.L¹¹ w  (XI)

M¹¹X¹¹ ₃.L¹¹ w  (XII)

wherein: M11 represents a lanthanoid element, scandium, or yttrium; X11each independently represent a hydrogen atom, a halogen atom, an alkoxygroup, a thiolate group, an amide group, a silyl group, an aldehyderesidue, a ketone residue, a carboxylic acid residue, a thicarboxylicacid residue, or a phosphorous compound residue; L11 represents a Lewisbase; and w represents 0 to 3.

Specific examples of a group (ligand) to form a bond to the rare earthelement of the rare earth element compound include: a hydrogen atom;aliphatic alkoxy groups such as a methoxy group, an ethoxy group, apropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxygroup, and a tert-butoxy group; aromatic alkoxy groups such as a phenoxygroup, a 2,6-di-tert-butylphenoxy group, a 2,6-diisopropylphenoxy group,a 2,6-dineopentylphenoxy group, a 2-tert-butyl-6-isopropylphenoxy group,a 2-tert-butyl-6-neopentylphenoxy group, and a2-isopropyl-6-neopentylphenoxy group; aliphatic thiolate groups such asthiomethoxy group, a thioethoxy group, a thiopropoxy group, athio-n-butoxy group, a thioisobutoxy group, a thio-sec-butoxy group, anda thio-tert-butoxy group; aryl thiolate groups such as a thiophenoxygroup, a 2,6-di-tert-butylthiophenoxy group, a2,6-diisopropylthiophenoxy group, a 2,6-dineopentylthiophenoxy group, a2-tert-butyl-6-isopropylthiophenoxy group, a2-tert-butyl-6-thioneopentylphenoxy group, a2-isopropyl-6-thioneopentylphenoxy group, and a2,4,6-triisopropylthiophenoxy group; aliphatic amide groups such as adimethyl amide group, a diethyl amide group, a diisopropyl amide group;arylamide groups such as a phenyl amide group, a 2,6-di-tert-butylphenylamide group, a 2,6-diisopropylphenyl amide group, a2,6-dineopentylphenyl amide group, a 2-tert-butyl-6-isopropylphenylamide group, a 2-tert-butyl-6-neopentylphenyl amide group, a2-isopropyl-6-neopentylphenyl amide group, and a 2,4,6-tert-butylphenylamide group; bistrialkylsilyl amide groups such as a bistrimethylsilylamide group; silyl groups such as a trimethylsilyl group, atris(trimethylsilyl)silyl group, a bis(trimethylsilyl)methylsilyl group,a trimethylsilyl(dimethyl)silyl group, and atriisopropylsilyl(bistrimethylsilyl)silyl group; halogen atoms such as afluorine atom, a chlorine atom, a bromine atom, and an iodine atom.Other examples may include: residues of aldehyde such assalicylaldehyde, 2-hydroxy-1-naphthaldehyde, and2-hydroxy-3-naphthaldehyde; residues of hydroxyphenone such as2′-hydroxyacetophenone, 2′-hydroxybutyrophenone, and2′-hydroxypropiophenone; residues of diketone such as acetylacetone,benzoylacetone, propionylaceton, isobutyl acetone, valerylacetone, andethylacetylacetone; residues of an carboxylic acid such as an isovalericacid, a caprylic acid, an octanoic acid, a lauric acid, a myristic acid,a palmitic acid, a stearic acid, an isostearic acid, an oleic acid, alinoleic acid, a cyclopentanecarboxylic acid, a naphthenic acid, anethylhexanoic acid, a pivalic acid, a versatic acid (trade name of aproduct manufactured by Shell Chemicals Japan Ltd., a synthetic acidcomposed of a mixture of C10 monocarboxylic acid isomers), aphenylacetic acid, a benzoic acid, 2-naphthoate acid, a maleic acid, anda succinic acid; residues of thicarboxylic acid such as a hexanethioicacid, 2,2-dimethylbutanethioic acid, a decanethioic acid, and athiobenzoic acid; residues of phosphoric acid ester such as a phosphoricacid dibutyl, a phosphoric acid dipentyl, a phosphoric acid dihexyl, aphosphoric acid diheptyl, a phosphoric acid dioctyl, phosphoric acidbis(2-ethylhexyl), a phosphoric acid bis(1-methylheptyl), a phosphoricacid dilauryl, a phosphoric acid dioleyl, a phosphoric acid diphenyl, aphosphoric acid bis(p-nonylphenyl), a phosphoric acid bis(polyethyleneglycol-p-nonylphenyl), a phosphoric acid(butyl)(2-ethylhexyl), aphosphoric acid(1-methylheptyl)(2-ethylhexyl), and a phosphoricacid(2-ethylhexyl)(p-nonylphenyl); residues of phosphonic acid estersuch as a 2-ethylhexyl phosphonic acid monobutyl, a 2-ethylhexylphosphonic acid mono-2-ethylhexyl, a phenylphosphonic acidmono-2-ethylhexyl, a 2-ethylhexyl phosphonic acid mono-p-nonylphenyl, aphosphonic acid mono-2-ethylhexyl, a phosphonic acidmono-1-methylheptyl, a and phosphonic acid mono-p-nonylphenyl; residuesof phosphinic acid such as a dibutylphosphinic acid, abis(2-ethylhexyl)phosphinic acid, a bis(1-methylheptyl)phosphinic acid,a dilauryl phosphinic acid, a dioleyl phosphinic acid, a diphenylphosphinic acid, a bis(p-nonylphenyl)phosphinic acid, abutyl(2-ethylhexyl) phosphinic acid,(2-ethylhexyl)(2-methylhexyl)(1-methylheptyl)phosphinic acid, an(2-ethylhexyl)(p-nonylphenyl) phosphinic acid, a butyl phosphinic acid,2-ethylhexyl phosphinic acid, a 1-methylheptyl phosphinic acid, an oleylphosphinic acid, a lauryl phosphinic acid, a phenyl phosphinic acid, anda p-nonylphenyl phosphinic acid. These ligands may be used alone or incombination of two or more.

As to the component (A) used in the second polymerization catalystcomposition, examples of the Lewis base to react with the rare earthelement compound may include: tetrahydrofuran; diethyl ether;dimethylaniline; trimethylphosphine; lithium chloride, neutral olefins,and neutral diolefins. Here, in the case where the rare earth elementcompound reacts with a plurality of Lewis bases (in the case where w is2 or 3 in Formulae (XI) and (XII)), the Lewis base L¹¹ in each Formulamay be the same as or different from each other.

The component (B) contained in the second polymerization catalystcomposition is at least one compound selected from a group consistingof: an ionic compound (B-1); an aluminoxane (B-2); and a halogencompound (B-3). The total content of the component (B) contained in thesecond polymerization catalyst composition is preferably in a range of0.1-fold mol to 50-fold mol, relative to the component (A).

The ionic compound represented by (B-1) is formed of non-coordinatinganion and cation, and an example thereof includes: an ionic compoundthat reacts with the component (A), i.e., a rare earth element compoundor a reactant of a rare earth element compound and a Lewis base, so asto form a cationic transition metal compound. Here, examples of thenon-coordinating anion include: tetraphenyl borate,tetrakis(monofluorophenyl)borate, tetrakis(difluorophenyl)borate,tetrakis(trifluorophenyl)borate, tetrakis(tetrafluorophenyl)borate,tetrakis(pentafluorophenyl)borate,tetrakis(tetrafluoromethylphenyl)borate, tetra(tolyl)borate,tetra(xylyl)borate, (triphenyl, pentafluorophenyl)borate,[tris(pentafluorophenyl), phenyl]borate, andtridecahydride-7,8-dicarbaundecaborate. Meanwhile, examples of thecation may include a carbonium cation, an oxonium cation, an ammoniumcation, a phosphonium cation, a cycloheptatrienyl cation, and aferrocenium cation containing a transition metal. Specific examples ofthe carbonium cation include trisubstituted carbonium cations such as atriphenylcarbonium cation and a tri(substituted phenyl)carbonium cation,and more specific examples of the tri(substituted phenyl)carboniumcation include a tri(methylphenyl)carbonium cation and atri(dimethylphenyl)carbonium cation. Examples of the ammonium cationinclude: trialkylammonium cations such as a trimethylammonium cation, atriethylammonium cation, a tripropylammonium cation, and atributylammonium cation (such as a tri(n-butyl)ammonium cation);N,N-dialkylanilinium cations such as a N,N-dimethylanilinium cation,N,N-diethylanilinium cation, and a N,N-2,4,6-pentamethylaniliniumcation; and dialkylammonium cations such as a diisopropylammonium cationand a dicyclohexylammonium cation. Specific examples of the phosphoniumcation include triarylphosphonium cations such as a triphenylphosphoniumcation, a tri(methylphenyl)phosphonium cation, and atri(dimethylphenyl)phosphonium cation. Therefore, the ionic compound maypreferably be a compound obtained by combining any one selected from thenon-coordinating anions described above and any one selected from thecations described above. Specific examples thereof preferably include aN,N-dimethylanilinium tetrakis(pentafluorophenyl)borate and atriphenylcarbonium tetrakis(pentafluorophenyl)borate. These ioniccompounds may be contained alone or in combination of two or more. Thecontent of the ionic compound in the second polymerization catalystcomposition is preferably 0.1-fold mol to 10-fold mol, and morepreferably about 1-fold mol, with respect to the component (A).

The aluminoxane represented by (B-2) is a compound obtained bycontacting an organic aluminum compound with a condensation agent, andexamples thereof include: a chain type aluminoxane or a cyclicaluminoxane, both having a repeating unit represented by the generalformula (—Al(R′)O—), wherein R′ is a hydrocarbon group having 1 to 10carbon atoms and may be partly substituted with halogen atom and/oralkoxy group, and the polymerization degree of the repeating unit ispreferably at least 5, more preferably at least 10. Here, specificexamples of R′ include a methyl group, an ethyl group, a propyl group,and isobutyl group, with the methyl group being preferred. Further,examples of the organic aluminum compound used as a raw material of thealuminoxane may include: trialkyl aluminums such as trimethyl aluminum,triethyl aluminum, triisobutyl aluminum and the like; and mixturesthereof, with the trimethyl aluminum being particularly preferred. Forexample, an aluminoxane obtained by using a mixture of trimethylaluminum and tributyl aluminum as a raw material can be suitably used.The content of aluminoxane in the second polymerization catalystcomposition is preferably about 10 to 1,000 at an element ratio (Al/M)of the aluminum element Al of the aluminoxane to the rare earth elementM forming the component (A).

The halogen compound represented by (B-3) includes at least one of: aLewis acid; a complex compound of a metal halide and a Lewis base; andan organic compound containing active halogen, and is capable ofreacting with, for example, the rare earth element compound as thecomponent (A) or with the reactant resulting from Lewis base and therare earth element compound, so as to form a compound, such as acationic transition metal compound, halogenated transition metalcompound or a compound with a charge-deficient transition metal center.The total content of the halogen compound in the second polymerizationcatalyst composition is preferably 1-fold mol to 5-fold mol, relative tothe component (A).

Examples of the Lewis acid may include: a boron-containing halogencompound such as B(C₆F₅)₃ and an aluminum-containing halogen compoundsuch as Al(C₆F₅)₃, and may also include a halogen compound containing anelement of Group III, Group IV, Group V, Group VI, and Group VIII of theperiodic table. Preferred examples thereof include an aluminum halide oran organometallic halide. Preferred examples of the halogen elementinclude chlorine and bromine. Specific examples of the Lewis acidinclude: a methyl aluminum dibromide; a methyl aluminum dichloride; anethyl aluminum dibromide; an ethyl aluminum dichloride; a butyl aluminumdibromide; a butyl aluminum dichloride; a dimethyl aluminum bromide; adimethyl aluminum chloride; a diethyl aluminum bromide; a diethylaluminum chloride; a dibutyl aluminum bromide; a dibutyl aluminumchloride; a methyl aluminum sesquibromide; a methyl aluminumsesquichloride; a ethyl aluminum sesquibromide; an ethyl aluminumsesquichloride; a dibutyltin dichloride; an aluminum tribromide; anantimony trichloride; an antimony pentachloride; a phosphorustrichloride; a phosphorus pentachloride; a tin tetrachloride; a titaniumtetrachloride; and tungsten hexachloride, with the diethyl aluminumchloride, the ethyl aluminum sesquichloride, the ethyl aluminumdichloride, the diethyl aluminum bromide, the ethyl aluminumsesquibromide, and the ethyl aluminum dibromide being particularlypreferred.

Preferred examples of the metal halide forming a complex compound of themetal halide and a Lewis base include: a beryllium chloride, a berylliumbromide; a beryllium iodide; a magnesium chloride; a magnesium bromide;a magnesium iodide; a calcium chloride; a calcium bromide; a calciumiodide; a barium chloride; a barium bromide; a barium iodide; a zincchloride; a zinc bromide; a zinc iodide; a cadmium chloride; a cadmiumchloride; a cadmium bromide; a cadmium iodide; a mercury chloride; amercury bromide; a mercury iodide; a manganese chloride; a manganesebromide; a manganese iodide; a rhenium chloride; a rhenium bromide; arhenium iodide; a copper chloride; a copper bromide; a copper iodide; asilver chloride; a silver bromide; a silver iodide; a gold chloride; agold iodide; and a gold bromide, with the magnesium chloride, thecalcium chloride, the barium chloride, the manganese chloride, the zincchloride, and the copper chloride being preferred, and the magnesiumchloride, the manganese chloride, the zinc chloride, and the copperchloride being particularly preferred.

Preferred examples of the Lewis base forming a complex compound of themetal halide and the Lewis base include: a phosphorus compound; acarbonyl compound; a nitrogen compound; an ether compound; and analcohol. Specific examples thereof include: a tributyl phosphate; atri-2-ethylhexyl phosphate; a triphenyl phosphate; a tricresylphosphate; a triethylphosphine; a tributylphosphine; atriphenylphosphine; a diethylphosphinoethane; an acetylacetone; abenzoylacetone; a propionitrileacetone; a valerylacetone; anethylacetylacetone; a methyl acetoacetate; an ethyl acetoacetate; aphenyl acetoacetate; a dimethyl malonate; a diphenyl malonate; an aceticacid; an octanoic acid; a 2-ethylhexoic acid; an oleic acid; a stearicacid; a benzoic acid; a naphthenic acid; a versatic acid; atriethylamine; a N,N-dimethylacetamide; a tetrahydrofuran; a diphenylether; a 2-ethylhexyl alcohol; an oleyl alcohol; stearyl alcohol; aphenol; a benzyl alcohol; a 1-decanol; and a lauryl alcohol, with thetri-2-ethylhexyl phosphate, the tricresyl phosphate; the acetylacetone,the 2-ethylhexoic acid, the versatic acid, the 2-ethylhexyl alcohol; the1-decanol; and the lauryl alcohol being preferred.

The Lewis base is subjected to reaction with the metal halide in theproportion of 0.01 to 30 mol, preferably 0.5 to 10 mol, per 1 mol of themetal halide. The use of the reactant obtained from the reaction of theLewis base can reduce residual metal in the polymer.

An example of the organic compound containing the active halogenincludes benzyl chloride.

The component (C) that may be contained in the second polymerizationcatalyst composition is an organic compound represented by the generalformula (X):

YR¹ _(a)R² _(b)R³ _(c)  (X)

wherein: Y is a metal selected from Group 1, Group 2, Group 12, andGroup 13 of the periodic table; R1 and R2 are the same or differenthydrocarbon groups each having 1 to 10 carbon atoms or a hydrogen atom;and R3 is a hydrocarbon group having 1 to 10 carbon atoms, in which R3may be the same as or different from R1 or R2 above, with a being 1 andb and c both being 0 when Y is a metal selected from Group 1 of theperiodic table, a and b being 1 and c being 0 when Y is a metal selectedfrom Group 2 and Group 12 of the periodic table, a, b, and c are all 1when Y is a metal selected from Group 13 of the periodic table. Theorganic metallic compound is preferably an organic aluminum compoundrepresented by the following general formula (Xa):

AlR¹R²R³  (Xa)

wherein: R¹ and R² are the same or different hydrocarbon groups eachhaving 1 to 10 carbon atoms or a hydrogen atom; and R³ is a hydrocarbongroup having 1 to 10 carbon atoms, in which R³ may be the same as ordifferent from R¹ or R² above. Examples of the organic aluminum compoundof the general formula (X) include: a trimethyl aluminum, a triethylaluminum, a tri-n-propyl aluminum, a triisopropyl aluminum, atri-n-butyl aluminum, a triisobutyl aluminum, a tri-t-butyl aluminum, atripentyl aluminum, a trihexyl aluminum, a tricyclohexyl aluminum, atrioctyl aluminum; a diethylaluminum hydride, a di-n-propyl aluminumhydride, a di-n-butyl aluminum hydride, a diisobutyl aluminum hydride, adihexyl aluminum hydride; a diisohexyl aluminum hydride, a dioctylaluminum hydride, a diisooctyl aluminum hydride; an ethyl aluminumdihydride, a n-propyl aluminum dihydride, and an isobutyl aluminumdihydride, with the triethyl aluminum, the triisobutyl aluminum, thediethyl aluminum hydride, and the diisobutyl aluminum hydride beingpreferred. The organic aluminum compounds as the component (C) may becontained alone or in combination of two or more. The content of theorganic aluminum compound in the second polymerization catalystcomposition is preferably 1-fold mol to 50-fold mol, and more preferablyabout 10-fold mol, with respect to the component (A).

—Third Polymerization Catalyst Composition—

The third polymerization catalyst composition includes themetallocene-based composite catalyst below and boron anion, and furtherpreferably includes another component such as a co-catalyst, which iscontained in a regular polymerization catalyst composition containing ametallocene complex. The third polymerization catalyst composition isalso referred to as two-component catalyst, which has themetallocene-based composite catalyst and boron anion. As is the casewith the metallocene-based composite catalyst, the third polymerizationcatalyst composition further contains boron anion, which allows thecontent of each monomer component in the copolymer to be arbitrarilycontrolled.

—Metallocene Catalyst—

One example of the metallocene-based composite catalyst is representedby the following formula (A):

R_(a)MX_(b)QY_(b)  (A)

wherein: R each independently represents an unsubstituted or substitutedindenyl group, the R being coordinated with M; M represent a lanthanoidelement, scandium, or yttrium; X each independently representshydrocarbon group having 1 to 20 carbon atoms, the X being μ-coordinatedwith M and Q; Q represents a Group 13 element in the periodic table; Yeach independently represents a hydrocarbon group having 1 to 20 carbonatoms or a hydrogen atom, the Y being coordinated with Q; and a and beach are 2.

One preferred example of the above-described metallocene-based compositecatalyst includes a metallocene-based composite catalyst represented bythe following formula (XV):

wherein: M¹ represents a lanthanoid element, scandium or yttrium; Cp^(R)each independently represents a nonsubstituted or substituted indenylgroup; R^(A) and R^(B) each independently represent a hydrocarbon grouphaving 1 to 20 carbon atoms, the R^(A) and R^(B) each beingμ-coordinated with M¹ and Al; and R^(C) and R^(D) each independentlyrepresent a hydrocarbon group having 1 to 20 carbon atoms or a hydrogenatom.

The use of the above metallocene-based polymerization catalyst enablesthe production of the polymer. The use of the metallocene-basedcomposite compounds such as an aluminum-based catalyst can reduce oreliminate the amount of alkyl aluminum to be used in the step ofsynthesizing the polymer. The use of a conventional catalyst systemwould require a large amount of alkyl aluminum to be used insynthesizing a polymer. For example, to obtain high catalytic effect,the metallocene-based composite catalyst of the present inventionrequires alkyl aluminum in an amount of only about 5 equivalents,whereas a conventional catalyst system would require alkyl aluminum inan amount of at least 10 equivalents, relative to a metal catalyst.

In the metallocene-based composite catalyst, the metal represented by Min the formula (A) is a lanthanoid element, scandium, or yttrium. Thelanthanoid elements include 15 elements with atomic numbers 57 to 71,and may be any one of them. Preferred examples of the central metalrepresented by M include samarium (Sm), neodymium (Nd), praseodymium(Pr), gadolinium (Gd), cerium (Ce), holmium (Ho), scandium (Sc), andyttrium (Y).

In the formula (A), R each independently represents an unsubstituted orsubstituted indenyl, the R being coordinated with the metal M. Specificexamples of the substituted indenyl group include a 1,2,3-trimethylindenyl group, a heptamethyl indenyl group, and a 1,2,4,5,6,7-hexamethylindenyl group.

In the formula (A), Q represents a Group 13 element in the periodictable. Specific examples thereof include boron, aluminum, gallium,indium, and thallium.

In the formula (A), X each independently represents a hydrocarbon grouphaving 1 to 20 carbon atoms, the X being μ-coordinated with M and Q.Here, examples of the hydrocarbon group having 1 to 20 carbon atomsinclude: a methyl group, an ethyl group, a propyl group, a butyl group,a pentyl group, a hexyl group, a heptyl group, an octyl group, a decylgroup, a dodecyl group, a tridecyl group, a tetradecyl group, apentadecyl group, a hexadecyl group, a heptadecyl group, and a stearylgroup. The μ-coordination refers to a state of coordination which formsa crosslinked structure.

In the formula (A), Y each independently represents a hydrocarbon grouphaving 1 to 20 carbon atoms or a hydrogen atom, the Y being coordinatedwith Q. Here, examples of the hydrocarbon group having 1 to 20 carbonatoms include, a methyl group, an ethyl group, a propyl group, a butylgroup, a pentyl group, a hexyl group, a heptyl group, an octyl group, adecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, apentadecyl group, a hexadecyl group, a heptadecyl group, and a stearylgroup.

In the formula (XV) above, the metal represented by M¹ is a lanthanoidelement, scandium, or yttrium. The lanthanoid elements include 15elements with atomic numbers 57 to 71, and may be any one of them.Preferred examples of the metal represented by M¹ include samarium (Sm),neodymium (Nd), praseodymium (Pr), gadolinium (Gd), cerium (Ce), holmium(Ho), scandium (Sc), and yttrium (Y).

In the formula (XV), Cp^(R) represents an unsubstituted or substitutedindenyl. Cp^(R) having an indenyl ring as a basic skeleton may berepresented by C₉H_(7-X)R_(X) or C₉H_(11-X)R_(X). Here, X represents aninteger of 0 to 7 or 0 to 11. R each independently preferably representsa hydrocarbyl group or a metalloid group. The hydrocarbyl grouppreferably has 1 to 20 carbon atoms, more preferably 1 to 10 carbonatoms, and still more preferably 1 to 8 carbon atoms. Preferred specificexamples of the hydrocarbyl group include a methyl group, an ethylgroup, a phenyl group, and a benzyl group. Examples of metalloid in themetalloid group include germyl (Ge), stannyl (Sn), and silyl (Si). Themetalloid group preferably has a hydrocarbyl group, and the examples ofsuch a hydrocarbyl group are similar to those listed above. Specificexample of the metalloid group includes a trimethylsilyl group.

Specific examples of the substituted indenyl group include 2-phenylindenyl and 2-methyl indenyl group. Two Cp^(R) in each of the generalformulae (I) and (II) may be the same as or different from each other.

In the formula (XV), R^(A) and R^(B) each independently represent ahydrocarbon group having 1 to 20 carbon atoms, and the R^(A) and R^(B)being μ-coordinated with M¹ and A¹. Here, examples of the hydrocarbongroup having 1 to 20 carbon atoms include, a methyl group, an ethylgroup, a propyl group, a butyl group, a pentyl group, a hexyl group, aheptyl group, an octyl group, a decyl group, a dodecyl group, a tridecylgroup, a tetradecyl group, a pentadecyl group, a hexadecyl group, aheptadecyl group, and a stearyl group. The μ-coordination refers to astate of coordination which forms a crosslinked structure.

In the formula (XV), R^(c) and R^(D) each independently represent ahydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom. Here,examples of the hydrocarbon group having 1 to 20 carbon atoms include, amethyl group, an ethyl group, a propyl group, a butyl group, a pentylgroup, a hexyl group, a heptyl group, an octyl group, a decyl group, adodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group,a hexadecyl group, a heptadecyl group, and a stearyl group.

The metallocene-based composite catalyst can be obtained by, forexample, reacting a metallocene complex with an organic aluminumcompound represented by AlR^(K)R^(L)R^(M) in a solvent. The metallocenecomplex is represented by the following formula (XVI):

wherein M² represents a lanthanoid element, scandium, or yttrium; Cp^(R)each independently represents an unsubstituted or substituted indenylgroup; R^(E) to R^(J) each independently represent an alkyl group having1 to 3 carbon atoms or a hydrogen atom; L represents a neutral Lewisbase; and w represents an integer of 0 to 3. The reaction may be carriedout at temperatures around room temperature, and thus themetallocene-based composite catalyst can be produced under mildconditions. The reaction time is arbitrary, but about several hours toseveral tens of hours. The reaction solvent is not particularly limited,but is preferably a solvent that is capable of dissolving the rawmaterial and the product. Toluene and hexane may for example be used.The structure of the metallocene-based composite catalyst may preferablybe determined by ¹H-NMR or X-ray crystallography.

In the metallocene complex represented by the formula (XVI), Cp^(R) isan unsubstituted indenyl or substituted indenyl, and is equivalent toCp^(R) in the formula (XV). Further, in the formula (XVI), the metal M²represents a lanthanoid element, scandium, or yttrium, which isequivalent to the metal M¹ in the formula (XV).

The metallocene complex represented by the formula (XVI) includes asilyl amide ligand represented by [—N(SiR₃)₂]. Groups represented by R(R^(E) to R^(J)) in the silyl amide ligand each independently representa hydrogen atom or an alkyl group having 1 to 3 carbon atoms. It ispreferred that at least one of R^(E) to R^(J) represents a hydrogenatom. With at least one of R^(E) to R^(J) representing a hydrogen atom,the catalyst can be synthesized with ease. Further, the alkyl group ispreferably a methyl group.

The metallocene complex represented by the above formula (XVI) furthercontains 0 to 3, preferably 0 or 1 neutral Lewis bases represented by L.Examples of the neutral Lewis base L include tetrahydrofuran, diethylether, dimethylaniline, trimethylphosphine, lithium chloride, neutralolefins, and neutral diolefins. When the complex includes a plurality ofneutral Lewis bases represented by L, the neutral Lewis bases L may bethe same as or different from each other.

The metallocene complex represented by the formula (XVI) may becontained as monomers, or as dimers or multimers having two or moremonomers.

The organic aluminum compound to be used for generating themetallocene-based composite catalyst is represented by a general formulaAlR^(K)R^(L)R^(M), where R^(K) and R^(E) each independently represent aunivalent hydrocarbon group having 1 to 20 carbon atoms or a hydrogenatom and R^(M) represents a univalent hydrocarbon group having 1 to 20carbon atoms, with the R^(M) being either the same as or different fromR^(K) or R^(E). Examples of the univalent hydrocarbon groups having 1 to20 carbon atoms include a methyl group, an ethyl group, a propyl group,a butyl group, a pentyl group, a hexyl group, a heptyl group, an octylgroup, a decyl group, a dodecyl group, a tridecyl group, a tetradecylgroup, a pentadecyl group, a hexadecyl group, a heptadecyl group, and astearyl group.

Specific examples of the organic aluminum compound include: a trimethylaluminum, a triethyl aluminum, a tri-n-propyl aluminum, a triisopropylaluminum, a tri-n-butyl aluminum, a triisobutyl aluminum, a tri-t-butylaluminum, a tripentyl aluminum, a trihexyl aluminum, a tricyclohexylaluminum, a trioctyl aluminum; a diethylaluminum hydride, a di-n-propylaluminum hydride, a di-n-butyl aluminum hydride, a diisobutyl aluminumhydride, a dihexyl aluminum hydride; a diisohexyl aluminum hydride, adioctyl aluminum hydride, a diisooctyl aluminum hydride; an ethylaluminum dihydride, a n-propyl aluminum dihydride, and an isobutylaluminum dihydride, with the triethyl aluminum, the triisobutylaluminum, the diethyl aluminum hydride, and the diisobutyl aluminumhydride being preferred. These organic aluminum compounds may becontained alone or in combination of two or more. The amount of theorganic aluminum compound to be used for generating themetallocene-based composite catalyst is preferably 1-fold mol to 50-foldmol, and more preferably about 10-fold mol, relative to the metallocenecomplex.

In the third polymerization catalyst composition, a specific example ofthe boron anion forming the two-component catalyst includes atetravalent boron anion. Examples thereof may include: a tetraphenylborate, a tetrakis(monofluorophenyl)borate, atetrakis(difluorophenyl)borate, a tetrakis(trifluorophenyl)borate, atetrakis(tetrafluorophenyl)borate, a tetrakis(pentafluorophenyl)borate,a tetrakis(tetrafluoromethylphenyl)borate, a tetra(tolyl)borate, atetra(xylyl)borate, a (triphenyl, pentafluorophenyl)borate, a[tris(pentafluorophenyl), phenyl]borate, and atridecahydride-7,8-dicarbaundecaborate, with thetetrakis(pentafluorophenyl)borate being preferred.

The boron anion may be used as an ionic compound combined with cation.Examples of the cation include a carbonium cation, an oxonium cation, anammonium cation, an amine cation, a phosphonium cation, acycloheptatrienyl cation, and a ferrocenium cation containing atransition metal. Examples of the carbonium cation includetrisubstituted carbonium cations such as a triphenylcarbonium cation anda tri(substituted phenyl)carbonium cation. Specific examples of thetri(substituted phenyl)carbonium cation include atri(methylphenyl)carbonium cation. Examples of the amine cation include:trialkylammonium cations such as a trimethylammonium cation, atriethylammonium cation, a tripropylammonium cation, and atributylammonium cation; N,N-dialkylanilinium cations such as aN,N-dimethylanilinium cation, a N,N-diethylanilinium cation, and aN,N-2,4,6-pentamethylanilinium cation; and dialkylammonium cations suchas a diisopropylammonium cation and a dicyclohexylammonium cation.Examples of the phosphonium cation include triarylphosphonium cationssuch as a triphenylphosphonium cation, a tri(methylphenyl)phosphoniumcation, and a tri(dimethylphenyl)phosphonium cation. Of those cations,the N,N-dialkylanilinium cations or the carbonium cations are preferred,and the N,N-dialkylanilinium cations are particularly preferred.Therefore, preferred examples of the ionic compound include aN,N-dimethylanilinium tetrakis(pentafluorophenyl)borate and atriphenylcarbonium tetrakis(pentafluorophenyl)borate. The content of theionic compound including a boron anion and a cation may preferably beadded by 0.1-fold mol to 10-fold mol, and more preferably by about1-fold mol, relative to the metallocene-based composite catalyst.

Although it is required to use the above metallocene-based compositecatalyst and the above boron anion in the third polymerization catalystcomposition, the presence of a boron anion in the reaction system forreacting the metallocene catalyst represented by the formula (XVI) withthe organic aluminum compound would not allow the synthesis of themetallocene-based composite catalyst of the formula (XV). Accordingly,preparation of the above-described third polymerization catalystcomposition requires the metallocene-based composite catalyst to besynthesized in advance and isolated and purified before combined with aboron anion.

Preferred examples of the co-catalyst that can be contained in the thirdpolymerization catalyst composition may include aluminoxanes, inaddition to the organic aluminum compound represented byAlR^(K)R^(L)R^(M). The aluminoxane is preferably an alkyl aluminoxane.Examples of the alkyl aluminoxane include methyl aluminoxane (MAO) andmodified methyl aluminoxanes. In addition, a preferred example of themodified methyl aluminoxane is MMAO-3A (manufactured by Tosoh FinechemCorporation). These aluminoxanes may be contained alone or incombination of two or more.

—Coupling Step—

The coupling step is a step for coupling at least parts (e.g., the endportions) of polymer chains of the synthesized polyisoprene obtained inthe polymerization step through a coupling reaction.

In the coupling step, coupling reaction is preferably performed when thepolymerization reaction reaches 100%.

The coupling agent used for the coupling reaction is not particularlylimited and may be selected as appropriate depending on the applicationthereof. Examples the coupling agent include, for example, (i) atin-containing compound, such as bis(maleicacid-1-octadecyl)dioctyltin(IV), (ii) an isocyanate compound, such as4,4′-diphenylmethanediisocyanate, and (iii) an alkoxysilane compound,such as glycidylpropyltrimethoxysilane. These coupling agents may beused alone or in combination of two or more thereof.

Among them, bis(maleic acid-1-octadecyl)dioctyltin(IV) is preferable interms of its high reaction efficiency and low gel-formation property.

The coupling reaction can increase the number average molecular weight(Mn).

The reaction temperature of the coupling reaction is not particularlylimited and may be selected as appropriate depending on the applicationthereof. The temperature is, however, preferably 10 to 100° C., and morepreferably 20 to 80° C.

The reaction temperature of 10° C. or higher can prevent a significantdecrease in reaction rate, and that of 100° C. or lower can prevent thegelation of polymers.

The reaction time of the coupling reaction is not particularly limitedand may be selected as appropriate depending on the application thereof.The reaction time is, however, preferably 10 minutes to 1 hour.

The reaction time of less than 10 minutes may fail to allow the reactionto proceed satisfactorily, and the reaction time exceeding 1 hour maycause the polymer to gel.

—Cleaning Step—

The cleaning step is a step for cleaning the polyisoprene obtained inthe polymerization step. The medium used in the cleaning is notparticularly limited and may be selected as appropriate depending on theapplication thereof. Examples of the medium include methanol, ethanol,and isopropanol. When a catalyst derived from a Lewis acid is used asthe polymerization catalyst, an acid (e.g. hydrochloric acid, sulfuricacid, and nitric acid) may be added to the solvent. The amount of acidthat may be added is preferably 15 mol % or less relative to thesolvent. An acid added by the amount exceeding 15 mol % can remain inthe polymer, potentially causing adverse effects on the reaction duringkneading and vulcanization.

This cleaning step suitably decreases the amount of residual catalystremaining in the synthesized polyisoprene.

<Isoprene Copolymer>

—Compounds Other than Isoprene—

Compounds other than isoprene that may be copolymerized with isopreneare not particularly limited and may be selected as appropriatedepending on the application thereof. Examples of such compoundsinclude, for example, a conjugated diene compound, such as1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl butadiene; aromatic vinylcompound, such as styrene; and an unconjugated olefin compound, such asethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and1-octene. These may used alone or in combination of two or more thereof.

Among them, butadiene and styrene are preferable in terms of controllingthe molecular weight.

—Cis-1,4 Bond Content—

The cis-1,4 bond content in a unit derived from the isoprene in theisoprene copolymer is not particularly limited and may be selected asappropriate depending on the application thereof. The bond content is,however, preferably 90% or more, more preferably 95% or more, and mostpreferably 98% or more.

The isoprene copolymer having cis-1,4 bond content of 90% or more candevelop strain-induced crystallinity satisfactorily

The isoprene copolymer having the cis-1,4 bond content within the above“more preferable” or “most preferable” range is advantageous in terms ofimproved durability related to the strain-induced crystallinity.

It should be noted that the cis-1,4 bond content here is not the ratioof the cis-1,4 bond to the whole isoprene copolymer but is the amount ofthe cis-1,4 bond in the unit derived from the isoprense.

—Trans-1,4 Bond Content—

The trans-1,4 bond content of the isoprene copolymer is not particularlylimited and may be selected as appropriate depending on the applicationthereof. The bond content is, however, preferably 10% or less, and morepreferably 5% or less.

The isoprene copolymer having trans-1,4 bond content of 10% or less candevelop strain-induced crystallinity satisfactorily.

The isoprene copolymer having the trans-1,4 bond content within theabove “more preferable” range is advantageous in terms of improveddurability related to the strain-induced crystallinity.

—3,4-Vinyl Bond Content—

The 3,4-vinyl bond content of isoprene in a unit derived from theisoprene in the isoprene copolymer is not particularly limited and maybe selected as appropriate depending on the application thereof. Thebond content is, however, preferably 5% or less, more preferably 2% orless.

The isoprene copolymer having the 3,4-vinyl bond content of 5% or lesscan develop strain-induced satisfactorily.

The isoprene copolymer having the cis-3,4-vinyl bond content within theabove “preferable” or “more preferable” range is advantageous in termsof durability related to the strain-induced crystallinity.

—Content of Isoprene-Derived Unit in Isoprene Copolymer—

The content of the unit derived from isoprene in the isoprene copolymeris not particularly limited and may be selected as appropriate dependingon the application thereof. The content is, however, preferably 5 to 95mol %.

The isoprene copolymer having 5 mol % or more isoprene-derived unitallows the isoprene to exhibit its properties satisfactorily, and thathaving 95 mol % or less isoprene-derived unit allows the copolymercomponent other than isoprene to exhibit the properties satisfactorily.For these reasons, the content of isoprene-derived unit being 5 to 95mol % is preferable.

—Chain Structure—

The chain structure is not particularly limited and may be selected asappropriate depending on the application thereof. Examples of the chainstructure include, for example, a block copolymer, a random copolymer, atapered copolymer, and an alternating copolymer.

—Block Copolymer—

The structure of the block copolymer is any one of (A-B)x, A-(B-A) x,and B-(A-B) x, wherein A is a block portion composed of monomer units ofisoprene, B is a block portion composed of monomer units of a compoundother than isoprene, and x is an integer of 1 or more. A block copolymercontaining multiple (A-B) or (B-A) structures is referred to as amulti-block copolymer.

—Random Copolymer—

The structure of the random copolymer has a random arrangement ofmonomer units of isoprene and monomer units of a compound other thanisoprene.

—Tapered Copolymer—

The tapered copolymer contains random copolymers and block copolymer ina mixed manner. Specifically, the tapered copolymer contains at leasteither a block portion (or block structure) composed of monomer units ofisoprene or a block portion composed of monomer units of a compoundother than isoprene, and a random portion (or random structure) composedof monomer units of isoprene and those of a compound other than isoprenethat are randomly arranged.

The structure of the tapered copolymer shows that the composition of theisoprene component and the compound component other than isoprene hascontinuous or discontinuous distribution.

—Alternating Copolymer—

The alternating copolymer contains isoprene units and units of acompound other than isoprene that are arranged alternately. Specificallythe structure of the alternating copolymer has a molecular chainstructure of -ABABABAB-, wherein A represents a monomer unit of isopreneand B represents a monomer unit of a compound other than isoprene.

—Method of Producing Isoprene Copolymer—

Next, a method of producing the isoprene copolymer will be described indetail. However, the manufacturing method described in detail below ismerely an example. The isoprene copolymer can be produced bypolymerizing isoprene monomers and monomers of a compound other thanisoprene in the presence of a polymerization catalyst or apolymerization catalyst composition.

The method of producing the isoprene copolymer of the present inventionincludes at least a polymerization step, and further includes coupling,cleaning, and other steps appropriately selected as necessary.

—Polymerization Step—

The polymerization step is a step for copolymerizing isoprene monomersand monomers of a compound other than isoprene.

In the polymerization step, isoprene monomers and monomers of a compoundother than isoprene can be copolymerized in a manner similar to thatconventionally used in producing polymers using a coordination ionpolymerization catalyst, except that the aforementioned polymerizationcatalyst, or the aforementioned first, second, or third polymerizationcatalyst composition is used. The polymerization catalyst or thepolymerization catalyst compositions used in the present invention havebeen already described in the above.

The catalyst that may be used in the polymerization step is theaforementioned polymerization catalyst, or the aforementioned first,second, or third polymerization catalyst composition.

An arbitrary method can be employed as the polymerization methodincluding, for example, solution polymerization, suspensionpolymerization, liquid phase bulk polymerization, emulsionpolymerization, vapor phase polymerization, and solid statepolymerization. In addition, in the case of using a solvent forpolymerization reaction, any solvent may be used that is inert to thepolymerization reaction, including, for example, toluene, cyclohexane,n-hexane and mixtures thereof.

In the case of using a polymerization catalyst composition, thepolymerization step can be carried out in either one of the followingmanners. That is, for example, (1) the components forming thepolymerization catalyst composition may be separately provided in thepolymerization reaction system containing isoprene monomers and monomersof a compound other than isoprene, to thereby prepare the polymerizationcatalyst composition in the reaction system, or (2) the polymerizationcatalyst composition prepared in advance may be provided into thepolymerization reaction system. Further, the manner (2) also includesproviding the metallocene complex (active species) activated by aco-catalyst.

Further, in the polymerization step, a terminator such as methanol,ethanol, and isopropanol may be used to stop the polymerization.

In the polymerization step, the polymerization reaction of the isopreneand a compound other than isoprene may preferably be performed in aninert gas atmosphere, and preferably in nitrogen or argon atmosphere.The polymerization temperature of the polymerization reaction is notparticularly limited, but preferably in a range of, for example, −100 to200° C., and may also be set to temperatures around room temperature. Anincrease in the polymerization temperature may reduce thecis-1,4-selectivity in the polymerization reaction. The polymerizationreaction is preferably performed under pressure in a range of 0.1 to10.0 MPa so as to allow the isoprene and the compound other thanisoprene to be sufficiently introduced into the polymerization system.Further, the reaction time of the polymerization reaction is notparticularly limited, but may preferably be in a range of, for example,1 second to 10 days, which may be selected as appropriate depending onthe conditions such as the type of the monomers to be polymerized, thetype of the catalyst, and the polymerization temperature.

—Coupling Step—

The coupling step is a step for denaturing end portions of the polymerchains of the isoprene copolymer obtained in the polymerization step, toperform coupling reaction.

In the coupling step, coupling reaction (or specifically denaturing theends of polymer chains) is preferably performed when the polymerizationreaction reaches 100%.

The coupling agent used for the coupling reaction is not particularlylimited and may be selected as appropriate depending on the applicationthereof. Examples the coupling agent include, for example, (i) atin-containing compound, such as bis(maleicacid-1-octadecyl)dioctyltin(IV), (ii) an isocyanate compound, such as4,4′-diphenylmethanediisocyanate, and (iii) an alkoxysilane compound,such as glycidylpropyltrimethoxysilane. These coupling agents may beused alone or in combination of two or more.

Among them, bis(maleic acid-1-octadecyl)dioctyltin(IV) is preferable interms of its high reaction efficiency and low gel-formation property.

The coupling reaction couples the polymer chains to provide polymershaving high molecular weight. The coupling reaction also inhibitsoccurrence of resolutions other than hydrolysis to minimize a decreasein the number average molecular weight (Mn).

The reaction temperature of the coupling reaction is not particularlylimited and may be selected as appropriate depending on the applicationthereof. The temperature is, however, preferably 10 to 100° C., and morepreferably 20 to 80° C.

The reaction temperature of 10° C. or higher can prevent a significantdecrease in reaction rate, and the reaction temperature of 100° C. orlower can prevent the gelation of polymers.

The reaction time of the coupling reaction is not particularly limitedand may be selected as appropriate depending on the application thereof.The reaction time is, however, preferably 10 minutes to 1 hour.

The reaction time of 10 minutes or longer allows the reaction to proceedsatisfactorily, and that of 1 hour or shorter can prevent the gelationof the polymers.

—Cleaning Step—

The cleaning step is a step for cleaning the isoprene copolymer obtainedin the polymerization step. The medium used in the cleaning is notparticularly limited and may be selected as appropriate depending on theapplication thereof. Examples of the medium include methanol, ethanol,and isopropanol.

(Rubber Composition)

The rubber composition of the present invention contains at least arubber ingredient, and further contains a filler, a crosslinking agent,and other components as necessary.

<Rubber Ingredient>

The rubber ingredient contains at least one of the synthesizedpolyisoprene and the isoprene copolymer, and further contains otherrubber ingredients as necessary.

The synthesized polyisoprene and the isoprene copolymer have beenalready described in detail in the above.

The content of the polymer contained in the rubber ingredient (i.e., thetotal amount (total content) of the synthesized polyisoprene, theisoprene copolymer, or the synthesized polyisoprene and the isoprenecopolymer) is not particularly limited and may be selected asappropriate depending on the application thereof. However, the contentis preferably 15 to 100% by mass.

The rubber ingredient having the total polymer content of 15 mass %allows the polymer to exhibit its properties satisfactorily.

—Other Rubber Ingredients—

The other rubber ingredients are not particularly limited and may beselected as appropriate depending on the application thereof. Examplesof such rubbers include butadiene rubber (BR), styrene butadiene rubber(SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber,ethylene-propylene rubber (EPM), ethylene-propylene unconjugated-dienerubber (EPDM), polysulfide rubber, silicone rubber, fluoro-rubber, andurethane rubber. These rubber ingredients may be used alone or incombination of two or more.

<Filler>

The filler is not particularly limited and may be selected asappropriate depending on the application thereof. Examples of the fillerinclude a carbon black and an inorganic filler. The rubber compositionpreferably contains at least one selected from the carbon black and theinorganic filler. More preferably, the rubber composition contains thecarbon black. The filler is added to the rubber composition to reinforcethe rubber composition.

The amount (content) of the filler contained in the rubber ingredient isnot particularly limited and may be selected as appropriate depending onthe application thereof. The content is, however, preferably 10 to 100mass parts, more preferably 20 to 80 mass parts, and most preferably 30to 60 mass parts, per 100 mass parts of the rubber ingredient.

The filler contained in an amount of 10 mass parts or more exhibits itseffect, and the filler contained in an amount of 100 mass parts or lesscan be reliably blended into the rubber ingredient. The filler containedin that amount can thus improve the performance of the rubbercomposition.

The rubber composition containing the filler in an amount within theabove “more preferable” or “most preferable” range is advantageous interms of balance of processability, low-loss performance, anddurability.

—Carbon Black—

The carbon black is not particularly limited and may be selected asappropriate depending on the application thereof. Examples of the carbonblack include FEF, GPF, SRF, HAF, N339, IISAF, ISAF, SAF. These carbonblacks may be used alone or in combination of two or more.

The nitrogen adsorption specific surface area of the carbon black, whichis determined according to N₂SA JIS K 6217-2: 2001, is not particularlylimited and may be selected as appropriate depending on the applicationthereof. However, it is preferably 20 to 150 m²/g, and more preferably35 to 145 m²/g.

The rubber composition having the carbon black with 20 m²/g or morenitrogen adsorption specific surface area (N₂SA) can preventdeterioration in durability of the obtained rubber, thereby achievingsufficient crack growth resistance. The rubber composition having thecarbon black with 100 m²/g or less nitrogen adsorption specific surfacearea (N₂SA) can improve low-loss performance, thereby enhancingworkability.

The content of the carbon black per 100 mass parts of the rubberingredient is not particularly limited and may be selected asappropriate depending on the application thereof. However, it ispreferably 10 to 100 mass parts, more preferably 10 to 70 mass parts,and most preferably 20 to 60 mass parts.

The rubber composition containing the carbon black in an amount of 10mass parts or more can prevent decline in breaking resistance caused byinsufficient reinforcement, and the rubber composition containing 100mass parts or less carbon black can prevent deterioration inprocessability and low-loss performance.

The rubber composition containing the carbon black in an amount withinthe above “more preferable” or “most preferable” range is advantageousin terms of maintaining a balance in each of the performances.

—Inorganic Filler—

The inorganic filler is not particularly limited and may be selected asappropriate depending on the application thereof. Examples of theinorganic filler include silica, aluminum hydroxide, clay, alumina,talc, mica, kaolin, glass balloon, glass beads, calcium carbonate,magnesium carbonate, magnesium hydroxide, magnesium oxide, titaniumoxide, potassium titanate, and barium sulfate. These inorganic fillersmay be used alone or in combination of two or more.

In using an inorganic filler, a silane coupling agent may also be usedas appropriate.

<Crosslinking Agent>

The crosslinking agent is not particularly limited and may be selectedas appropriate depending on the application thereof. Examples of thecrosslinking agent include a sulfur-containing crosslinking agent, anorganic peroxide-containing crosslinking agent, an inorganiccrosslinking agent, a polyamine crosslinking agent, a resin crosslinkingagent, a sulfur compound-based crosslinking agent, anoxime-nitrosamine-based crosslinking agent, and sulfur, with thesulfur-containing crosslinking agent being more preferred as the rubbercomposition for a tire.

The content of the crosslinking agent is not particularly limited andmay be selected as appropriate depending on the application thereof. Thepreferred content thereof is, however, 0.1 to 20 mass parts per 100 massparts of the rubber ingredient.

The rubber composition containing the crosslinking agent in an amount of0.1 mass parts or more can develop crosslinking, and the rubbercomposition containing the crosslinking agent in an amount of 20 massparts or less can prevent the crosslinking that may be caused by part ofthe crosslinking agent during kneading, and can prevent the loss ofphysical properties of vulcanizate.

<Other Components>

The rubber composition may further contain a vulcanization acceleratorin addition to the above components. Examples of compounds that can beused as the vulcanization accelerator include guanidine-based compounds,aldehyde-amine-based compounds, aldehyde-ammonia-based compounds,thiazole-based compounds, sulfenamide-based compounds, thiourea-basedcompounds, thiuram-based compounds, dethiocarbamate-based compounds, andxanthate-based compounds.

Further, if necessary, any known agent such as a softening agent, avulcanizing co-agent, a colorant, a flame retardant, a lubricant, afoaming agent, a plasticizer, a processing aid, an antioxidant, an ageresister, an anti-scorch agent, an ultraviolet rays protecting agent, anantistatic agent, a color protecting agent, and other compounding agentmay be used according to the intended use thereof.

(Crosslinked Rubber Composition)

The crosslinked rubber composition according to the present invention isnot particularly limited as long as being obtained by crosslinking therubber composition of the present invention, and may be selected asappropriate depending on the application thereof.

The conditions of the crosslinking are not particularly limited and maybe selected as appropriate depending on the application thereof.However, a preferred temperature is 120 to 200° C. and a preferredheating time is 1 to 900 minutes.

(Tire)

The tire of the present invention is not particularly limited as long asit contains the crosslinked rubber composition of the present invention,and may be selected as appropriate depending on the application thereof.

The crosslinked rubber composition of the present invention may be usedin any portion of the tire, and the portion may be selected asappropriate depending on the application thereof. Examples of theportion include, for example, a tread, a base tread, a sidewall, a sidereinforcing rubber, and a bead filler.

Among these portions, the crosslinked rubber composition used in a treadis advantageous in terms of durability.

The tire can be produced by using a conventional method. For example, acarcass layer, a belt layer, a tread layer, which are composed ofunvulcanized rubber and/or cords, and other members used for theproduction of usual tires are successively laminated on a tire moldingdrum, then the drum is withdrawn to obtain a green tire. Thereafter, thegreen tire is heated and vulcanized in accordance with an ordinarymethod, to thereby obtain a desired tire (for example a pneumatic tire).

(Applications Other than Tires)

The crosslinked rubber composition of the present invention may be usedfor applications other than tires, such as anti-vibration rubber,seismic isolation rubber, a belt (conveyor belt), a rubber crawler, andvarious types of hoses.

EXAMPLES

In the following, the present invention will be described in furtherdetail with reference to Examples. However, the present invention is inno way limited to the following Examples.

Producing Example 1 Method of Producing Polymer A

To obtain polymer A, 6.2 μmol oftris[bis(trimethylsilyl)amide]gadolonium Gd[N(SiMe₃)₂]₃, 3.22 mmol oftriisobutylaluminum, and 5.0 g of toluene were placed in a 1 Lpressure-resistant glass reactor in a glove box under nitrogenatmosphere, and the compounds were aged for 30 minutes. Subsequently,6.2 μmol of triphenylcarbonium tetrakis(pentafluorophenyl)borate(Ph₃CB(C₆F₅)₄) and 472.0 g of cyclohexane were placed in the reactor andthe compounds were further aged for 30 minutes. The reactor was thentaken out from the glove box, and 120.0 g of isoprene was added to thereactor. Polymerization was then performed at room temperature for 12hours. After the polymerization, 1 mL of an isopropanol solutioncontaining 2,2′-methylene-bis(4-ethyl-6-t-butylphenol) (NS-5) in anamount of 5 mass % was added to the reactor to stop the reaction. Largeamounts of methanol were further added to the reactor to isolate thepolymers, and the isolated polymers were vacuum dried at 70° C. toobtain polymer A. The yield of polymer A thus obtained was 103.0 g.

Producing Example 2 Method of Producing Polymer B

To obtain polymer B, 4.65 μmol oftris[bis(trimethylsilyl)amide]gadolonium Gd[N(SiMe₃)₂]₃, 0.70 mmol ofdiisobutylaluminum hydride, and 5.0 g of toluene were placed in a 1 Lpressure-resistant glass reactor in a glove box under nitrogenatmosphere, and the compounds were aged for 30 minutes. Subsequently,4.65 μmol of triphenylcarbonium tetrakis(pentafluorophenyl)borate(Ph₃CB(C₆F₅)₄) and 378.0 g of cyclohexane were placed in the reactor andthe compounds were further aged for 30 minutes. The reactor was thentaken out from the glove box, and 127.5 g of isoprene was added to thereactor. Polymerization was then performed at room temperature for 3hours. After the polymerization, 1 mL of an isopropanol solutioncontaining 2,2′-methylene-bis(4-ethyl-6-t-butylphenol) (NS-5) in anamount of 5 mass % was added to the reactor to stop the reaction. Largeamounts of methanol were further added to the reactor to isolate thepolymers, and the isolated polymers were vacuum dried at 70° C. toobtain polymer B. The yield of polymer B thus obtained was 99.0 g.

Producing Example 3 Method of Producing Polymer C

To obtain polymer C, 50.0 μmol oftris[bis(trimethylsilyl)amide]gadolonium Gd[N(SiMe₃)₂]₃, 0.50 mmol oftriisobutylaluminum, and 50.0 g of toluene were placed in a 1 Lpressure-resistant glass reactor in a glove box under nitrogenatmosphere, and the compounds were aged for 30 minutes. Subsequently,50.0 μmol of triphenylcarbonium tetrakis(pentafluorophenyl)borate(Ph₃CB(C₆F₅)₄) and 300.0 g of normal hexane were placed in the reactorand the compounds were further aged for 30 minutes. The reactor was thentaken out from the glove box, and 50.0 g of isoprene was added to thereactor. Polymerization was then performed at room temperature for 3hours. After the polymerization, 1 mL of an isopropanol solutioncontaining 2,2′-methylene-bis(4-ethyl-6-t-butylphenol) (NS-5) in anamount of 5 mass % was added to the reactor to stop the reaction. Largeamounts of methanol were further added to the reactor to isolate thepolymers, and the isolated polymers were vacuum dried at 70° C. toobtain polymer C. The yield of polymer C thus obtained was 23.0 g.

Polymers A to C prepared as above and isoprene rubber (trade name:IR2200, JSR Corporation) were measured and evaluated with the followingmethod to investigate the microstructure (cis-1,4 bond content), thenumber average molecular weight (Mn), and the molecular weightdistribution (Mw/Mn). The results are shown in Table 1.

In addition, the gel fractions and the amount of residual catalysts ofPolymers A to C prepared as above and polyisoprene rubber (trade name:IR2200, JSR Corporation) were also measured and evaluated with thefollowing method. The results are also shown in Table 1.

<Method of Analyzing Polymer>

(1) Microstructure (Cis-1,4 Bond Content)

The microstructures were calculated from the integral ratio between thepeaks obtained from ¹H-NMR and ¹³C-NMR [¹H-NMR: δ4.6-4.8 (═CH₂ of3,4-vinyl unit), 5.0-5.2 (—CH═ of 1,4-unit); ¹³C-NMR: δ23.4 (1,4-cisunit), 15.9 (1,4-trans unit), 18.6 (3,4-unit)]. The number averagemolecular weights (Mn) and molecular weight distributions (Mw/Mn) wereobtained by GPC by using polystyrene as a standard substance.

(2) Number Average Molecular Weight (Mn) and Molecular WeightDistribution (Mw/Mn)

The number average molecular weights (Mn) and molecular weightdistributions (Mw/Mn) were measured by gel permeation chromatography[GPC: HLC-8020 (manufactured by Tosoh Corporation)] by using arefractometer as a detector, and calculated in terms of polystyrene byreferencing monodisperse polystyrene as a standard. The column was GMHXL(manufactured by Tosoh Corporation), the elute was tetrahydrofuran, andthe measurement temperature was 40° C.

(3) Gel Fraction

To determine the gel fraction, 12 mg of sample polymers were placed insample bottles containing 5 cc of tetrahydrofuran, and the sample bottlewere allowed to stand overnight. The solutions were then passed througha 0.45 μm PTFE filter, and GPC measurement was conducted. The sampleareas (mV) of RI obtained by GPC measurement were divided by sampleweights used to calculate the percentage.

<Amount of Residual Catalyst>

The amount of residual catalyst (i.e., amount of residual metal) wasmeasured by performing elemental analysis.

TABLE 1 Polymer A Polymer B Polymer C IR2200 Mn (×10³) 586 775 2,390 341Mw/Mn 2.68 2.63 2.19 4.87 Cis-1,4 bond content (%) 98.2 97.6 96.9 95.0Amount of residual catalyst 280 60 220 530 (ppm) Gel fraction (%) 15 1414 25

<Method of Evaluating Rubber Composition>

Vulcanized rubber obtained by preparing and vulcanizing the rubbercomposition having the compounding formulation shown in Table 2 wasevaluated by the following method to measure (1) breaking resistance and(2) abrasion resistance. The results are shown in Table 3.

(1) Breaking Resistance (Expressed by Index)

A tensile test was conducted at room temperature in accordance with JISK 6301-1995 to measure the tensile strength (Tb) of the vulcanizedrubber compositions. The tensile strengths, expressed by an indexobtained by determining the tensile strength of Comparative Example as100, are shown in Table 3. A greater index value indicates betterbreaking resistance.

(2) Abrasion Resistance (Expressed by Index)

The amount of abrasion was measured with a Lambourn abrasion testingmachine at a slip rate of 60% at room temperature. The abrasionresistance was expressed by an index obtained by using the reciprocal ofthe ratio of the abrasion amount of Example to that of ComparativeExample. A greater index value indicates better abrasion resistance.

TABLE 2 Component Mass part Master batch Polymer *1 50.0 Natural rubber(NR) *2 50.0 Carbon black ISAF *3 45.0 Stearic acid 2.0 Wax *4 2.0Antioxidant 6C *5 1.0 Final batch Zinc white 3.0 Vulcanizationaccelerator TBBS *6 1.0 Sulfur 1.4 *1: Polymers A to C and polyisoprenerubber (trade name: IR2200, manufactured by JSR Corporation) *2: RSS #3*3: Seast 6 (manufactured by Tokai Carbon Co., Ltd.) *4:Microcrystalline wax: Ozoace0280 (manufactured by Nippon Seiro Co.,Ltd.) *5: N-(1,3-dimethylbutyl)-N′-p-phenylenediamine, NOCRAC 6C(manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) *6:N-tert-butyl-2-benzothiazilsulfenicamide, NOCCELER NS (manufactured byOuchi Shinko Chemical Industrial Co., Ltd.)

TABLE 3 Comparative Example 1 Example 2 Example 3 Example Polymer APolymer B Polymer C IR2200 Breaking resistance 106 103 110 100 Abrasionresistance 104 103 112 100

Table 3 shows that, in the synthesized polyisoprene contained in therubber composition, the polymer containing a residual catalyst in anamount of 300 ppm or less can provide a crosslinked rubber compositionwith improved durability (i.e, breaking resistance, abrasion resistance,and crack growth resistance).

INDUSTRIAL APPLICABILITY

The polymer and the rubber composition containing the polymer of thepresent invention can be suitably used in, for example, tire members,particularly in the tread member of tire.

1. A polymer being a synthesized polyisoprene or an isoprene copolymer,the polymer has residual catalyst derived from a catalyst used inpolymerization in an amount of 300 ppm or less.
 2. The polymer accordingto claim 1, wherein the catalyst includes a catalyst derived from aLewis acid.
 3. The polymer according to claim 1, having a number averagemolecular weight (Mn) of 1.5 million or more when measured by gelpermeation chromatography (GPC).
 4. A rubber composition comprising arubber ingredient that at least contains the polymer according toclaim
 1. 5. The rubber composition according to claim 4, wherein therubber ingredient contains the polymer in an amount of 15 to 100 mass %in total.
 6. The rubber composition according to claim 4, furthercomprising a filler, wherein the rubber composition contains the fillerin an amount of 10 to 100 mass parts per 100 mass parts of the rubberingredient.
 7. A tire having the rubber composition according to claim6.
 8. A tire comprising a tread member having the rubber compositionaccording to claim 6.